setjast í helgan stein

In old Icelandic the meaning of this idiom was "to join a monastery". In older times the adjective helgur ("holy") wasn't in the idiom however, and it was simply used in the form setjast í stein ("to sit in a stone") or ganga í stein ("join a stone"), whereas the word stone referred to a monastery. Literally meaning "to sit in a holy stone", from setjast ("to sit") + í ("in") + helgan, accusative masculine of helgur ("sacred, holy") + stein, the accusative singular of steinn ("stone").